For the analysis of complex molecules one often uses tandem mass spectrometers (MS-MS systems) in which
1. the first-stage mass spectrometer separates the precursor-molecule ion from ions of different masses.
2. the precursor-molecule ions are shot into a dissociation medium (for instance a gas collision cell or a gas jet, a solid or a liquid surface or a dense cloud of electrons or ions) where these precursor molecules fractionate, usually after excitations of internal vibrations.
3. the second-stage mass spectrometer that analyzes the masses of the fragment ions (i.e., the ionized daughter molecules).
The most powerful but also most expensive MS-MS systems consist for the time being mostly of two double-focusing sector-field mass spectrometers. However, there are also very successful other combinations of systems in which quadrupole mass spectrometers but also ion traps or Fourier-transform mass spectrometers are employed. For all these second-stage systems it is very time consuming to scan through the full spectrum of the masses of the daughter molecules. In several cases sector-field mass spectrometers have therefore been equipped with some type of an "electronic photoplate" in which all ions in a certain mass range are recorded simultaneously. A problem, however, is that using a quadrupole mass spectrometer as the second-stage mass analyzer often limits one to the registering of a limited number of mass lines.